nLCode is signed, so check for > 0

Change-Id: I2e40d020d088679a8f9d197485a782d511012bd5
Reviewed-on: https://gerrit.libreoffice.org/39657Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

sw/source/filter/ww8/ww8par3.cxx

@@ -220,7 +220,7 @@ eF_ResT SwWW8ImplReader::Read_F_FormListBox( WW8FieldDesc* pF, OUString& rStr)
 {
     WW8FormulaListBox aFormula(*this);
 
-    if (pF->nLCode && rStr.getLength() >= pF->nLCode && rStr[pF->nLCode-1] == 0x01)
+    if (pF->nLCode > 0 && rStr.getLength() >= pF->nLCode && rStr[pF->nLCode-1] == 0x01)
         ImportFormulaControl(aFormula,pF->nSCode+pF->nLCode-1, WW8_CT_DROPDOWN);
 
     const SvtFilterOptions& rOpt = SvtFilterOptions::Get();